JP2003147209A - Resin composition for optical element, optical element and projection screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resin composition for optical elements capable of suppressing collapse due to adhesion of mutual surfaces of the optical elements and scuff by vibration during transportation, especially vibration under the low-temperature environment and the optical elements composed of the improved resin composition for the optical elements and a projection screen. SOLUTION: The resin composition constituting a Fresnel lens sheet 2 or a lenticular lens sheet 3 composing the projection screen 1 is subjected to regulation of values of the storage modulus of elasticity, the temperature corresponding to the maximum value of loss tangent and the equilibrium modulus of elasticity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for an optical element, which is defined by parameters relating to glass transition temperature and viscoelasticity, and an optical element composed of this resin composition. The present invention relates to a resin composition for an optical element, in which the surface is not deformed or destroyed, or the abrasion is minimized. Further, the present invention, when the optical element is used in combination with another optical member such as a lenticular lens sheet, can minimize the abrasion or abrasion of the surface of the optical member due to the optical element. It also relates to a projection screen consisting of a possible optical element and a combination with a lenticular lens sheet.

[0002]

2. Description of the Related Art An optical element has an optical element surface in which a layer of a resin composition having an optical shape is laminated on a transparent base material, in addition to the base material, or has an optical element surface. Without having it, the resin composition layer has an optical element surface in which an optical shape is directly provided. Although there are various optical shapes on the surface of the optical element, many optical elements formed by using a resin composition have a large number of irregularities in which fine lens shapes are arranged and viewed as a whole. .

When an optical element is used, a plurality of optical elements may be used in combination. When two or more optical elements are used in combination, the effect is maximized and the optical element is used. In order to protect the surfaces, it is often the case that the surfaces of the optical elements face each other and are brought into close contact with each other. The most typical example is the case of a Fresnel lens sheet and a lenticular lens sheet in a projection screen. Usually, each Fresnel lens surface (which is a circular Fresnel convex lens) and the lenticular lens surface are used in close contact with each other. .

As described above, when the optical elements are brought into close contact with each other on their surfaces, each of them has an uneven surface, so that they affect each other. For example, in the above-mentioned typical example, the cross-sectional shape of the Fresnel lens surface is a saw-tooth shape and the tip is sharp, and the cross-sectional shape of the lenticular lens surface has a roundness such as a circle or a part of an ellipse. It was a sensation. When the Fresnel lens sheet having such a cross-sectional shape and the lenticular lens sheet come into close contact with each other, the raised top of the lenticular lens,
Since the sharp tip of the Fresnel lens comes into contact, when contact pressure is applied, the shape of the lenticular lens and / or the Fresnel lens, that is, the concavo-convex shape of the optical element surface may be deformed.

The crushing of the shape of the lens as described above can be eliminated by increasing the hardness of the resin forming the lens, but if the hardness is simply increased, the lens is likely to be chipped during handling or cutting, On the contrary, since it causes a problem, it is desirable to increase the hardness while leaving a viscous element.

Further, the hardness of the resin is generally closely related to the glass transition temperature (Tg), but if the glass transition temperature (Tg) of the resin is too low, rubber elasticity cannot be obtained and pressure is applied. Leads to plastic deformation. Normal,
If it has a certain degree of crosslink density, rubber elasticity is exhibited even if the glass transition temperature is low, and even if pressure is applied, plastic deformation does not occur, but in the resin composition for optical elements, If it is attempted to lower the glass transition temperature and increase the crosslink density, a rigid chain composed of a benzene ring or an alicyclic group will be introduced to improve the refractive index, which is essential for optical elements. Causing an increase in the transition temperature,
On the other hand, the direction of increasing the glass transition temperature is advantageous in terms of improving the refractive index, but if the glass transition temperature is too high, the rigidity becomes too high, and as a result, the lens sheet may be curved. Become. To easily increase the refractive index, if a material containing a halide such as bromide or sulfur is used, it is possible to formulate without relying on the benzene ring, etc., and it is possible to control mechanical properties well. However, considering the load on the environment, it is better to avoid using it as much as possible.

In addition to the deformation in the static state as described above,
When an optical element in a state where the optical element surfaces are in close contact with each other is transported, a shift vibration in a direction in which the optical elements are displaced from each other is added during transportation for a long time, and thus scratches are generated in a dynamic state in which they are rubbed with each other. Since the internal temperature of the shipping container and the cargo container is always increased or decreased, the degree of deformation and scratches is further amplified by the high and low temperatures generated by these.

For example, during transportation in cold regions such as North America, Northern Europe or northeastern China, the hardness of the resin forming the optical element surface increases with a decrease in temperature, so that scratches occur. It becomes easier, and even more remarkable among the resins when an ultraviolet curable resin having a large hardness temperature dependency is used.

In Japanese Unexamined Patent Publication No. 10-10647, the elastic modulus of the resin of a lens sheet made of a cured active energy ray-curable resin is from 80 to 80 at -20 ° C to 40 ° C.
It is disclosed that the optical performance is maintained by defining the amount to 20000 kg / cm ² . However, in this publication, there is no description demonstrating whether or not the trouble caused by the rubbing of the lens sheets during transportation at -20 ° C has been resolved.

[0010]

Therefore, in the present invention, conventionally, deformation such as crushing due to the close contact between the optical element surfaces of the optical element, and deviation vibration during transportation, especially deviation vibration at low temperature, are caused. To provide a resin composition for an optical element capable of suppressing the occurrence of scratches, particularly effectively suppressing the latter occurrence of scratches, and an optical element constituted by such an improved resin composition for an optical element. Another object is to provide a projection screen.

[0011]

Means for Solving the Problems The above-mentioned problems are stipulated by defining the storage elastic modulus of the dynamic viscoelasticity of the resin at a low temperature which is assumed as the environmental temperature during transportation, By defining the equilibrium modulus,
The above problems have been solved.

A first aspect of the present invention is for constructing an optical element, which has a storage modulus of dynamic viscoelasticity at −20 ° C. of 2.96 × 10 ¹⁰ dyne / cm ² or less and a loss tangent. ~ The temperature corresponding to the maximum value of the loss tangent in the temperature curve is 35 ° C to 71 ° C, and the equilibrium elastic modulus is 1.1.
3 × 10 ⁸ dyne / cm ^{2 to} 4.79 × 10 ⁸ dyne
It is related with the resin composition for optical elements characterized by being / cm < ² >. A second invention is to configure an optical element, wherein the storage modulus of dynamic viscoelasticity at −20 ° C. is 2.96 × 10 ¹⁰ dyne / cm ² or less, and loss tangent to temperature curve. The temperature corresponding to the maximum value of the loss tangent is 21.0 ° C. to 35 ° C., and the equilibrium elastic modulus is 6.12 × 10 ⁷ dyne / cm ^{2 to} 2.98 × 1.
The present invention relates to a resin composition for an optical element, which is 0 ⁸ dyne / cm ² . A third invention is the first invention, wherein the loss tangent at −20 ° C. is 0.012.
The present invention relates to a resin composition for an optical element characterized by the above. A fourth invention is the same as the second invention,
The present invention relates to a resin composition for an optical element, which has a loss tangent at -20 ° C of 0.02 or more.
A fifth invention relates to the resin composition for an optical element according to any one of the first to fourth inventions, which has a dynamic friction coefficient at room temperature of 0.07 to 0.15. A sixth invention relates to an optical element characterized in that the resin composition for an optical element according to any one of the first to fifth inventions is wholly or partially constituted. A seventh invention relates to the optical element according to the sixth invention, characterized in that the optical element is a Fresnel lens sheet. An eighth invention relates to a projection screen including the optical element of the sixth or seventh invention and a lenticular lens sheet.

[0013]

FIG. 1 is a schematic view showing a projection screen using a Fresnel lens sheet which is a typical optical element of the present invention. The projection screen 1 includes a Fresnel lens sheet 2 and a lenticular lens sheet 3. Are installed so as to face the respective lens surfaces 2c and 3c and are in close contact with each other.
In FIG. 1, in each of the lens sheets 2 and 3, the lens layers 2b and 3b are illustrated as being laminated on the base materials 2a and 3a, respectively. But this is not another layer,
It may be integrated. Further, as shown in FIG. 1, the lenticular lens sheet 3 may have a small lenticular lens, a protrusion and a black stripe on the surface opposite to the Fresnel lens sheet 2 side.

The optical element may have any optical shape such as a Fresnel concave lens, a prism, or a fly's eye lens in addition to the lenticular lens and Fresnel (convex) range described with reference to FIG. . Further, one optical element may have optical element surfaces of the same kind or different kinds of optical shapes on both surfaces thereof.

In the present invention, in order to form the entire optical element, or in the case where the optical element has a lens layer on the substrate, in order to form the lens layer, various types as described below are used. A specific optical element resin composition defined by parameters is used. The optical element composed of the resin composition for a specific optical element is typically a Fresnel lens sheet, and such an optical element, particularly the Fresnel lens sheet, may be combined with a lenticular lens sheet to form a projection screen. it can. In addition, the resin composition for an optical element here is directly
For the product condition, or for measurement, it means a thin resin plate or a lens layer. However,
If it is in the state of the raw material before manufacturing the product, and if it is in the state of the product, or if it is made into a thin plate for measurement, various parameters as described below can be satisfied. It also includes an uncured composition.

The resin composition for optical elements is an ionizing radiation-curable substance mainly composed of an oligomer and / or a monomer of an ionizing radiation-curable radical-polymerizable acrylate compound, or a cationic-polymerizable epoxy compound. Alternatively, it is preferable that an oligomer and / or a monomer of an oxetane compound is used as a raw material, and if necessary, additives for curing such as an ultraviolet polymerization initiator and a sensitizer are mixed. The additives for curing are decomposed when the resin composition undergoes polymerization, and thus those decomposed products remain in the state of the product. Further, a thermoplastic resin may be blended for the purpose of improving the properties of the obtained product.

Further, the resin composition for optical elements may be mixed with various additives which can be added at the time of producing an ordinary sheet-shaped or plate-shaped resin product,
Further, for the purpose of improving the optical performance of the optical element, a light diffusing agent, a coloring agent or the like may be added.

The parameters defining the resin composition for an optical element of the present invention are (1) storage elastic modulus, (2) loss tangent-temperature corresponding to the maximum value of loss tangent in a temperature curve (provisionally Tp). , And (3) equilibrium elastic modulus, and if necessary, (4) loss tangent and (5) dynamic friction coefficient as parameters.

Among the above, (1) to (4),
Obtained from the results of dynamic viscoelasticity measurement. In order to obtain (1) to (4), a resin sheet made of a resin composition for an optical element having a predetermined thickness is prepared as a sample. When a resin sheet is prepared using the ultraviolet curable resin composition, it is irradiated with ultraviolet rays to be cured. For the measurement, a dynamic viscoelasticity measuring device is used, and the storage elastic modulus and the loss tangent are measured while changing the temperature and applying vibration at a constant cycle in the long axis direction of the sample. From the relationship between the obtained storage elastic modulus and temperature, it may be more appropriate to determine (1) storage elastic modulus at a predetermined temperature, particularly -20 ° C, and (3) equilibrium elastic modulus (equilibrium storage elastic modulus). No.) Also,
From the obtained relationship between loss tangent and temperature, the temperature (Tp) corresponding to the maximum value of (4) loss tangent and (2) loss tangent at a predetermined temperature, particularly -20 ° C, is obtained.

In order to obtain (5) above, a sample similar to the above resin sheet was used as a sample, and a surface tester capable of measuring dynamic friction / static friction was used to apply a load to the ball indenter while Measurement is performed by sliding the surface at a constant speed, and the measured load divided by the vertical load is taken as the dynamic friction coefficient.

The resin composition for an optical element of the present invention comprises -20
Storage modulus at ℃ 2.96 × 10 ⁹ dyne /
It is desirable that it is not more than cm ² . The storage elastic modulus relates to the ability to elastically store energy with respect to a strain applied to a material exhibiting viscoelasticity. The larger this value is, the harder it becomes against vibration. Here, the storage elastic modulus at −20 ° C. is 2.9.
When it exceeds 6 × 10 ⁹ dyne / cm ² , it is likely to be scratched when transported while the optical element surfaces are in contact with each other in a low temperature environment near −20 ° C.

Incidentally, there is a loss elastic modulus as a parameter related to the storage elastic modulus, and by increasing the loss elastic modulus at a low temperature, that is, by increasing the ability of a material to dissipate stress as heat, a scratch at a low temperature can be obtained. It is also possible to reduce the occurrence of. However, even if the storage elastic modulus is reduced as in the present invention instead of increasing the loss elastic modulus, it is possible to reduce the occurrence of scratches at low temperatures. In the case of increasing the loss modulus of the former, it results in increasing the viscous structure in the bulk of the material when forming an optical element, which induces plastic deformation when a static external force is exerted, and Although the drawback that the surface of the optical element such as the surface is likely to be crushed is inevitable, this drawback can be avoided when the storage elastic modulus is reduced.

The resin composition for an optical element of the present invention has a preferable range of temperature (Tp) corresponding to the maximum value of the loss tangent to the loss tangent in the temperature curve. The temperature (Tp) corresponding to the maximum value of the loss tangent to the loss tangent in the temperature curve is said to represent the phase transition of the material,
It almost corresponds to the glass transition point which represents the transition from the glass region to the rubber region.

The resin composition for an optical element of the present invention has a temperature (Tp) corresponding to the maximum value of (A) loss tangent to the maximum loss tangent in the temperature curve, in addition to the above-mentioned limitation of the storage elastic modulus at -20 ° C. Is 35 ° C. to 71 ° C., and the equilibrium elastic modulus is 1.13 × 10 ⁸ dyne / cm ^{2 to} 4.79 × 10.
⁸ dyne / cm ² or (B) loss tangent ~
The temperature corresponding to the maximum value of the loss tangent on the temperature curve (T
p) is 21.0 ° C. to 35 ° C., and the equilibrium elastic modulus is 6.12 × 10 ⁷ dyne / cm ^{2 to} 2.98 × 10 ⁸ d.
It is preferably yne / cm ² .

When the temperature is outside the range of (A) or (B), for example, when the temperature (Tp) corresponding to the maximum value of the loss tangent to the loss tangent in the temperature curve is larger than the specified value, the equilibrium is reached. There is also a balance with the elastic modulus, but because the hardness of the resin composition for optical elements is hard, it is easily scratched at low temperatures, and when it is smaller than the specified value, the resin composition for optical elements is soft. When the optical element surfaces come into contact with each other, it is unavoidable that the concave and convex shapes of the optical element surfaces are deformed. Also, when the equilibrium elastic modulus is larger than the specified value, if the optical element surfaces are transported in contact with each other in a low temperature environment near -20 ° C, scratches are likely to occur,
Further, when the value is smaller than the specified value, when the optical element surfaces are in contact with each other, it is unavoidable that the uneven shape of the optical element surface is deformed.

The resin composition for an optical element of the present invention has the above-mentioned storage modulus of dynamic viscoelasticity at -20 ° C.
In addition to the provision of the temperature (Tp) corresponding to the maximum value of the loss tangent in the loss tangent to temperature curve, and the equilibrium elastic modulus,
It is more preferable that the lower limit of the loss tangent at 20 ° C. be specified.

The above-mentioned storage modulus of dynamic viscoelasticity at -20 ° C. and the temperature (Tp) corresponding to the maximum value of the loss tangent in the above-mentioned (A) to the loss tangent in the temperature curve,
And has a specified value of the equilibrium modulus, −
The loss tangent at 20 ° C. is preferably 0.012 or more. Further, the storage modulus of dynamic viscoelasticity at −20 ° C., the temperature (Tp) corresponding to the maximum value of the loss tangent in the above-mentioned (B) to the loss tangent in the temperature curve, and the specified value of the equilibrium elastic modulus are shown. If you have -20
The loss tangent at 0 ° C. is preferably 0.02 or more.

The peak value of the loss tangent in the loss tangent-temperature curve is 1.5 or less, more preferably 1.2 or less, and when these values are exceeded, the equilibrium elastic modulus in the rubber region decreases. It will have to be done and crushing will occur easily.

In the present invention, the upper limit of the storage elastic modulus of the dynamic viscoelasticity of the resin composition for an optical element at -20 ° C. is set, so that the optical element surfaces are protected from each other in a low temperature environment near -20 ° C. It prevents the generation of scratches when transported in contact, but at this temperature, in addition to the ability to elastically store energy and the ability to dissipate as heat, it will be around -20 ° C. It can help prevent scratches that occur during transportation in air. In both cases (A) and (B) above, when the loss tangent at -20 ° C is below the above lower limit, the prevention of scratches that occur during transportation at around -20 ° C is not promoted.

The resin composition for an optical element of the present invention has the above-mentioned storage modulus of dynamic viscoelasticity at -20 ° C.,
Loss tangent to temperature (Tp) corresponding to the maximum value of loss tangent in the temperature curve, equilibrium elastic modulus at 80 ° C., and −
In addition to defining the lower limit of loss tangent at 20 ° C., it is more preferred that the dynamic friction coefficient at room temperature be defined, which helps prevent scratches that occur during transportation at around −20 ° C.

Here, the room temperature refers to 25 ° C., but even at 20 ° C., it does not substantially affect the value of the dynamic friction coefficient. The value of the dynamic friction coefficient is 0.07-
0.15 is preferable, and when the upper limit is exceeded, −
The effect of promoting the prevention of scratches generated during transportation at around 20 ° C is poor, and if the amount is less than the lower limit, it is necessary to considerably increase the amount of a sliding agent such as silicone. Especially when used in various temperature environments,
When used in a high temperature environment, the slip agent is likely to bleed out to the outside, which makes it difficult to maintain the optical performance of the optical element.

In order to realize the above dynamic friction coefficient, it is preferable to add a slip agent (or slip agent) to the resin composition for optical elements. As the slip agent, optical inhibition with respect to the resin composition for optical elements, for example, without bleeding out of the slip agent in the high temperature environment test or a decrease in transmittance, migration to the surface occurs during molding, Bleed out does not occur after curing, the refractive index of light with the resin composition constituting the resin composition for optical elements is as close as possible, or the particle size is not visible at the wavelength of light or less, When accompanied by a transparent substrate, it is preferably one that does not impair the adhesion with the transparent substrate.

As the slip agent, silicone, silicone polymer, preferably modified silicone, more preferably polyether modified polydimethylsiloxane can be used.

Specifically, product numbers manufactured by BYK Japan KK; BYK-307, BYK-333, B
YK-332, BYK-331, BYK-345, BY
K-348, BYK-370, product numbers manufactured by Shin-Etsu Chemical Co., Ltd .; X-22-2404, KF-62-7192, K
F-615A, KF-618, KF-353, KF-3
53A, KF-96, KF-54, KF-56, KF-
410, KF-412, HIVAC F-4, HIVA
C F-5, KF-945A, KF-354, KF-3
53, manufactured by Toray Dow Corning Japan KK, product numbers; SH-28PA, SH-29PA, SH-190,
SH-510, SH-550, SF8410, SF84
21, SYLGARD 309, BY16-152, BY
16-152B, BY16-152C, product numbers FZ-2105, FZ-2165, FZ manufactured by Nippon Unica Co., Ltd.
-2163, L-77, L-7001, L-7002,
L-7604, L-7607, product numbers manufactured by EFKA Additives; EFKA-S018, EFKA-3033,
EFKA-83, EFKA-3232, EFKA-32
36, EFKA-3239, or Kyoeisha Yushi Kagaku Co., Ltd. product name; Granol 410, etc.

In addition, in order to reduce bleed-out due to environmental changes after curing, reactive silicone such as silicone acrylate or silicone methacrylate may be used in combination. As a specific reactive silicone, a product number manufactured by Big Chemie Japan KK; B
YK-UV3500, BYK-UV3510, BYK-
UV3530, Painted UV manufactured by Nippon Unica Co., Ltd.
-31, or Shin-Etsu Chemical Co., Ltd. product number; X-2
4-8201, X-22-174DX, X-22-24
26, X-22-2404, X-22-164A, X-
22-164B, X-22-164C, X-21-30
There are 56 mag.

[0036]

[Examples] The following shows the results of making samples using the resin composition and measuring the above-mentioned various parameters, and the results of practical evaluation of the Fresnel lens sheet. As the parameters, the storage elastic modulus at each temperature, the loss tangent at each temperature, the equilibrium elastic modulus, the maximum value of the loss tangent, and the dynamic friction coefficient, and the refractive index and the compression elastic modulus are shown for reference. As the evaluation results, the results of screen crushing and vibration test at each temperature are shown. Especially for items for which temperature is not specified,
Temperature; determined at 25 ° C.

[Preparation of Sample for Measuring Dynamic Viscoelasticity] A sample for measuring dynamic viscoelasticity of storage elastic modulus, loss tangent and equilibrium elastic modulus was prepared as follows. First, 40
A stainless steel plate having a flat surface whose temperature was controlled to 40 ° C to 42 ° C was used as a mold, and the ultraviolet curable resin composition whose temperature was controlled to 40 ° C to 42 ° C was applied to the surface of the mold so that the thickness was 200 µm. Using a metal halide type ultraviolet lamp (manufactured by Nippon Batteries Co., Ltd.), cumulative light amount: 2000 mJ / cm ² ,
Irradiation was performed under conditions of a peak illuminance of 250 mW / cm ² to cure the resin composition, and then the cured sheet was peeled off to obtain a sample sheet.

[Preparation of Sample for Measuring Compressive Elastic Modulus] Preparation of the sample for measuring the compressive elastic modulus is similar to the preparation of the sample for measuring the dynamic viscoelasticity, except that a stainless steel plate having a flat surface is used. In place of the Fresnel lens, a nickel mold having an inverted Fresnel lens shape was used to obtain a sample sheet having the Fresnel lens shape.

[Measurement of Dynamic Viscoelasticity] A dynamic viscoelasticity measuring apparatus (manufactured by Orientec Co., Ltd., “Reo Vibron”) was used by using the sample for dynamic viscoelasticity measurement prepared as described above.
By applying a load strain of 0.05% to a strip sample of 30 mm x 3 mm x 0.2 mm, 1 to 10H in the long axis direction.
Applying forced vibration of frequency z, at a heating rate of 3 ° C / min,
While raising the set temperature between -100 ° C and 100 ° C,
The storage elastic modulus and the loss tangent were measured to obtain a storage elastic modulus-temperature curve and a loss tangent-temperature curve.

From the obtained storage elastic modulus to temperature curve, 25
The storage elastic modulus at each temperature of ° C (normal temperature), 0 ° C, and -20 ° C was obtained. Separately from this, the frequency of forced vibration is set to 1 Hz, and the storage elastic modulus to temperature curve obtained in the same manner as above from the other, the storage elastic modulus at 80 ° C. when Tp described below is less than 60, When Tp was 60 ° C. or higher, the storage elastic modulus at 100 ° C. was regarded as the equilibrium elastic modulus.

From the obtained loss tangent-temperature curve,
The loss tangent at each temperature of 25 ° C (normal temperature), 0 ° C, and -20 ° C was obtained. In addition, the temperature at which the loss tangent was the maximum was obtained and set as Tp (loss tangent-temperature corresponding to the maximum value of the loss tangent on the temperature curve).

[Measurement of dynamic friction coefficient] Using a sample prepared by the same procedure as the sample for dynamic viscoelasticity measurement except that the thickness was 100 μm and the sample was covered with an acrylic plate and irradiated with ultraviolet rays, the surface property was measured. Dressing (Shinto Kagaku Co., Ltd., Haydon
Tripogear type; 14DR), vertical load (100g point pressure) is applied with a ball indenter, and 300mm / m
The surface of the sample was slid at a speed of in, measurement was performed 5 times, and the average value was taken.

[Measurement of Refractive Index] As a sample, a cured sheet prepared in the same manner as the sample for dynamic viscoelasticity measurement was used, and the sample was prepared by using 1-bromonaphthalene in the prism portion of the Abbe refractometer. Adhere closely, set the sample temperature to 25 ° C,
The refractive index was measured.

[Measurement of Compressive Elastic Modulus] To measure the compressive elastic modulus, an ultra-fine hardness tester (H-10, manufactured by Fischer GmbH, Germany) is used.
The universal hardness test using 0V) is applied, the load by the indenter is gradually increased to a predetermined value, and then gradually decreased to obtain the load-penetration depth curve, and analyzed from this result. The compressive elastic modulus was determined by. A ball indenter made of tungsten carbide (WC) having a radius R of 0.4 mmφ was used as the indenter.

The load-penetration depth curve is typically as shown in FIG.
It shows the appearance as shown in. First, when the load f is gradually increased from the point of zero load, deformation occurs and the penetration depth of the indenter gradually increases. When the load increase is stopped at a certain load value, the penetration due to plastic deformation stops, as at the point, and when the load value is maintained as it is, the creep depth continues to increase and the penetration depth increases. It reaches the point where the maintenance of the value is stopped. After that, when the load is gradually reduced, the penetration depth decreases toward the point due to elastic deformation.

In the above, the maximum load value F, which is the load value at the point in FIG. 2, was set to 20 mN. The contact pressure between the Fresnel lens sheet and the lenticular lens sheet in an actual projection screen is small and difficult to measure, but if the deformation of the lens sheet forming the screen is about 10 μm at the outer peripheral portion of the lens sheet under severe conditions. Since the performance of the lens is acceptable, the load required to deform the conventionally used lens sheet by 10 μm is about 20 mN, and therefore the maximum load value is determined as such. The time for creep deformation was appropriately set to 60 seconds.

After all, the procedure for obtaining the load-penetration depth curve is as follows. (1) Increase the load value for compression from 0 to 20 mN in 100 steps every 0.1 seconds. (2) A load value of 20 mN is maintained for 60 seconds to cause creep deformation. (3) Decrease in 40 steps every 0.1 seconds until the load value reaches 0.4 mN (test machine minimum load). (4) Maintain the load value of 0.4 mN for 60 seconds to recover the penetration depth. (5) The above (1) to (4) are repeated three times. As shown in FIG. 3, the parts on which the ball indenter acts are the individual subdivided lens surfaces constituting the Fresnel lens, such as 2c, 2c ′, and 2 in FIG.
It is preferable that it is near the center of the portion indicated by c ″.
Then, it is near the position corresponding to P / 2. Also in the case of other lens shapes, it is preferable to act the ball indenter near the center of each lens surface forming the lens.

The compressive elastic modulus (E) is obtained by the following formula. E = (2h ^* (2R-h ^* )- ^{1/2 *} H ^* ([Delta] H / [Delta] f)-(1-n) / e = 1 / (5.586 * h ^** H ^* ([Delta] H / [Delta] f)- 7.813 × 10 ⁻⁷ where h ^* is the load-penetration depth curve of the load reduction area (area surrounded by points, points, and H in FIG. 3) when the load f is the maximum value F Tangent line and penetration depth axis (horizontal axis)
It is the penetration depth (unit: mm) at the intersection with. R is the radius of the tip of the indenter (R = 0.4 mm). H is the maximum value of the penetration depth h (unit: mm). ΔH / Δf is the reciprocal of the slope of the load-penetration depth curve of the load reduction area (area surrounded by points, points, and H in FIG. 3) when the load f is the maximum value F. n is the material of the ball indenter (W
Poisson's ratio (n = 0.22) of C). e is the elastic modulus of the material (WC) of the ball indenter (e = 5.3 × 10 ⁵ N
/ Mm ² ) 0.22). As described in the preceding paragraph, the load increase / decrease and the like are repeated three times in the order of (1) to (4), and the load-penetration depth curve is obtained each time, and the compression elastic modulus (E) ( The unit; Mpa) is calculated, and the average value is calculated.

[Evaluation of Screen Collapse] The Fresnel lens sheet and the lenticular lens sheet are adhered to each other at their lens surfaces, and the four sides are fixed with an adhesive tape.
A projection screen was embedded in a V-screen size wooden frame, mounted on a projection TV set, and a white screen was projected by a projector. After this projection was continued for 1 hour, the screen was observed again. The environmental temperature was 25 ° C. In the observation, the case where the uneven brightness due to the collapse of the lens shape was clearly observed was evaluated as ×, the case where the uneven brightness was recognized but not noticeable was evaluated as Δ, and the case where the uneven brightness was not observed was evaluated as ○.

[Vibration Test] A Fresnel lens sheet and a lenticular lens sheet are adhered to each other at their lens surfaces, the four sides are fixed with adhesive tape, and a TV screen-sized wooden frame is fixed at a constant temperature. A vibration tester (Akasi Co., Ltd., vibration tester, EDS252) installed in an environmental test chamber capable of maintaining The vibration condition is PSD (Power Specru) shown in FIG.
m Density) random wave shown in the waveform, 43
With 20 seconds as one cycle, a test corresponding to a truck transportation of 5000 km is conducted at a temperature of 25 ° C. for 10 cycles,
Five cycles were performed at a temperature of 0 ° C., and three cycles were performed at a temperature of −20 ° C. This random wave is an uncertain wave having statistical properties, and its properties can be expressed by a PSD function. In this vibration test, the test conditions are determined using the function as an index. The use of such a random wave can eliminate the non-linear element of the vibration, that is, the non-linear element due to the mounting of the projection screen, the packaging form, etc. can be eliminated to excite the vibration of the object under a certain condition. Because it will be possible. Further, the vibrations are all different on any time axis when the test start time is 0, and therefore a situation closer to the vibration during actual transportation can be created. The environmental temperature is 25 ° C (normal temperature), 0
C. and -20.degree. C. After the test was completed, when a white screen was projected by a projector, the uneven brightness due to rubbing was clearly observed, and the uneven brightness was not noticeable. The case where no brightness unevenness was observed was evaluated as ◯.

As a result of the measurement of the above various parameters,
The results of practical evaluation of the Fresnel lens sheet are shown in the following "Table 1" to "Table 3". In "Table 1" to "Table 3", sample symbols A to P relate to Examples, and Q relates to Comparative Examples.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

According to the invention of claim 1 or 2, since the storage elastic modulus, Tp, and the equilibrium elastic modulus are defined, the optical elements are rubbed by vibration while they are in close contact with each other. Even in the case, it is possible to configure an optical element that is unlikely to be crushed or scratched, and is particularly resistant to scratch even when the optical elements are rubbed by vibration while in close contact with each other in a low temperature environment near -20 ° C. A resin composition for optical elements can be provided. According to the invention of claim 3 or claim 4, in addition to the effect of the invention of claim 1 or claim 2 cited respectively, in a low temperature environment of around -20 ° C, vibration is caused while the optical elements are in close contact with each other. It is possible to provide a resin composition for an optical element that is more resistant to scratches even when it is rubbed. According to the invention of claim 5, in addition to the effect of the invention of any one of claims 1 to 4, since the dynamic friction coefficient is defined, even if the optical elements vibrate while they are in close contact with each other, by sliding, It is possible to provide a resin composition for an optical element capable of suppressing the occurrence of scratches. According to invention of Claim 6, 1st-5th
Since the optical element is composed of the resin composition for an optical element of any one of the inventions, it is possible to provide an optical element capable of exhibiting the effect of each resin composition for an optical element. According to the invention of claim 7, since the optical element is a lenticular lens sheet having a saw-tooth cross section and a sharp tip,
It is possible to provide an optical element in which the same effect as that of the invention of claim 6 can be more clearly exhibited. According to the invention of claim 8, it is possible to provide a projection screen including an optical element capable of exerting the effect of the invention of claim 6 or claim 7 and a lenticular lens sheet.

[Brief description of drawings]

FIG. 1 is a diagram showing a projection screen which is an optical element.

FIG. 2 is a diagram for explaining a load-penetration depth curve.

FIG. 3 is a diagram showing a portion on which an indenter acts.

FIG. 4 is a graph of a PSD waveform used in a vibration test.

[Explanation of symbols]

1 Projection screen 2 Fresnel lens sheet 3 Lenticular lens sheet

Claims (8)

[Claims] 1. A structure for forming an optical element, which has a storage elastic modulus of dynamic viscoelasticity at -20 ° C. of 2.9.
It is 6 × 10 ¹⁰ dyne / cm ² or less, and the temperature corresponding to the maximum value of the loss tangent to the loss tangent in the temperature curve is 35.
℃ ~ 71 ℃ and equilibrium elastic modulus 1.13 × 10 ⁸
A resin composition for an optical element, wherein the resin composition is dyne / cm ^{2 to} 4.79 × 10 ⁸ dyne / cm ² . 2. A structure for forming an optical element, which has a storage modulus of dynamic viscoelasticity at -20 ° C. of 2.9.
It is 6 × 10 ¹⁰ dyne / cm ² or less, and the temperature corresponding to the maximum value of the loss tangent to the loss tangent in the temperature curve is 2
1.0 ° C. to 35 ° C., and equilibrium elastic modulus is 6.12 ×
10 ⁷ dyne / cm ^{2 to} 2.98 × 10 ⁸ dyne / c
m ² is a resin composition for an optical element. 3. The loss tangent at −20 ° C. is 0.012.
It is above, The resin composition for optical elements of Claim 1 characterized by the above-mentioned. 4. The resin composition for an optical element according to claim 2, which has a loss tangent at −20 ° C. of 0.02 or more. 5. The coefficient of dynamic friction at room temperature is 0.07 to
It is 0.15, The resin composition for optical elements in any one of Claims 1-4. 6. An optical element comprising the resin composition for an optical element according to any one of claims 1 to 5, which is wholly or partially constituted. 7. The optical element according to claim 6, wherein the optical element is a Fresnel lens sheet. 8. A projection screen comprising the optical element according to claim 6 or 7, and a lenticular lens sheet.